The transfer of data from field sheets to computer files always involves the risk of errors being made in plant symbols or other identifying codes. If a master list of symbols or codes is incorporated into the software programs used for data entry on CRT computer terminals the risk of making errors can be substantially reduced. This is done by utilizing the highly time efficient binary search to compare each entered symbol or code with the master list. Detection of errors before the data are transferred to computer files saves much time which would otherwise be spent in retrieving and correcting files.